1. Field of the Invention
This invention generally relates to an apparatus for converting wave energy into electrical energy, and, more in particular, to a power generating apparatus for generating electrical power utilizing wave motion. More specifically, the present invention relates to a wave-activated power generating apparatus having a backwardly open duct which is open backwardly with respect to the advancing direction of waves relative to the apparatus.
2. Description of the Prior Art
A wave-activated power generating apparatus is currently used in the form of a buoy as a nautical mark. One example of such a wave-activated power generating buoy is schematically shown in FIG. 1. As shown, the wave-activated power generating buoy 1 includes a pipe 3 which is immersed vertically downward with respect to the water surface. The pipe 3 has a bottom end 4 opened downwardly and there is formed an air chamber 2 together with the water surface in the vicinity of a top end of the pipe. Above the air chamber 2 is provided a valve chamber 5, whose interior is divided into an upper chamber 5a and a lower chamber 5b. An air turbine 6 and a power generator 7 driven by the air turbine 6 are provided inside of the upper chamber 5a. On the other hand, in the side walls of the upper chamber 5a and the lower chamber 5b of the valve chamber 5 are provided an appropriate number of valves 8 capable of being opened and closed. The upper chamber 5a is in fluidic communication with the lower chamber 5b via a through-hole 5c. Thus, as the water surface inside of the pipe 3 moves up and down due to wave motion, the air inside of the air chamber 2 flows into the atmosphere through the lower chamber 5b and the upper chamber 5a as indicated by the arrow in FIG. 1, whereby this air flow is utilized to rotate the air turbine 6 thereby driving the generator 7 to generate power.
In the structure shown in FIG. 1, the pipe 3 typically has a length of approximately 4 meters and provides the maximum specific pressure (pressure head inside of the air chamber 2/wave height) of approximately 0.3 at the throttling ratio (nozzle cross sectional area/cross sectional area of the air chamber 2)=1/100.
Another example of a wave-activated power generating apparatus is schematically shown in FIG. 2. This example is constructed in the form of a ship-shaped buoy as a large-scale implementation. The ship-shaped buoy 9 is provided with a front opening 9a at the bow thereof and a side opening 9b at each side thereof. Although not shown, the ship-shaped buoy 9 is also provided with a duct which is in fluidic communication with all of these front and side openings and also with an air chamber, which is associated with an air turbine. In this case, the front or bow of the ship-shaped buoy 9 is connected to mooring means so that the front opening 9a and also side openings 9b are directed generally opposite to the advancing direction of waves. With such a structure, the specific pressures in the order of 0.3 (at the front opening 9a) and 0.15 (at the side opening 9b ) are obtained at the throttling ratio of 1/100. It is to be noted, however, that the mooring force is extremely high because the front opening 9a is directed opposite to the advancing direction of travelling waves.
The power generating buoy shown in FIG. 1 has the pipe 3 which extends downwardly and thus it cannot be used in shallow waters. On the other hand, the power generating apparatus shown in FIG. 2 requires high mooring force and thus it has problems under harsh weather conditions, such as stormy weather, though it may be used in shallow waters. Under the circumstances, there has been proposed a wave-activated power generating apparatus 10 having a backwardly open duct as shown in FIG. 3. As shown, the apparatus 10 of FIG. 3 includes a floatable buoy main body 11 and a front float 12. The apparatus 10 also includes an L-shaped duct 14 having a horizontally extending portion 14a and a vertically extending portion 14b. The horizontally extending portion 14a has one end connected in fluidic communication to the bottom end of the vertically extending portion 14b and the other end open backwardly and thus directed in the same direction as the advancing direction of waves with respect to the apparatus 10. An air chamber 15 is defined at the top end of the vertically extending portion 14b so that the air inside of the air chamber 15 is periodically compressed due to the relative motion between the column of water inside of the duct 14 and the duct 14. A nozzle opening 16 is defined at the top of the air chamber 15 so that the compressed air is discharged out of this nozzle opening 16, thereby driving to rotate an air compressor (not shown). The vertically extending portion 14b is located between the buoy main body 11 and the front float 12. The structure shown in FIG. 3 may be used in shallow waters and the mooring force can be avoided to become excessive because the opening 14c is directed backwardly with respect to the advancing direction of waves. A more detailed description of the type of the apparatus 10 shown in FIG. 3 may be found in U.S. Ser. No. 619,632, pending, filed June 14, 1984, entitled "WAVE-ACTIVATED POWER GENERATOR", partially assigned to the applicant of this application.